JPH0251865B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a refractory used for a mold injection port connecting a mold and a tundish in continuous casting equipment. [Conventional technology] Conventionally, reaction-sintered silicon nitride and hot-pressed boron nitride have been used as connection refractories, but silicon nitride (Si ₃ N ₄ ) has problems with spalling in the initial stage of casting. Also, boron nitride (BN) has low hardness, so there are problems with wear resistance. To improve these drawbacks, add 3 to 40% BN to Si ₃ N ₄ .
In order to improve thermal shock resistance by incorporating
120575), or means to improve thermal shock resistance and corrosion resistance such as Si ₃ N ₄ -AlN-BN system (Japanese Patent Laid-Open No. 120575)
-129666). For example, in horizontal continuous casting equipment, as shown in FIG. The molten steel 5 inside is injected into the mold 4 through the field nozzle 2 and the connecting refractory 3, where it is cooled and drawn out while forming a solidified shell 6. The connecting refractory 3 used in this continuous casting equipment is easy to process because it requires particularly high thermal shock resistance, difficulty in getting wet with molten steel, high corrosion resistance, and high dimensional accuracy. Performance such as certain things is required. For this reason, it has been known to use hot-pressed BN sintered bodies or reaction-sintered Si ₃ N ₄ sintered bodies, but hot-pressed BN sintered bodies have low hardness,
There are problems with wear resistance. In addition, reaction-sintered Si ₃ N ₄ sintered bodies _have little dimensional change after sintering, have high strength, and can be manufactured at low cost, making them promising materials as a resistant material for _horizontal continuous casting. Due to its low thermal shock resistance, BN is added to improve it, and aluminum nitride (AlN) is used to improve its corrosion resistance.
These methods have no problem in short-time casting of carbon steel, but they have problems with long-term casting of carbon steel or casting of stainless steel. Therefore, there is a technology to further improve corrosion resistance by adding Al ₂ O ₃ and sintering it at high temperature to form a sialon-based solid solution.
Even in this case, there is a problem of melting loss when stainless steel is cast for a long time. [Problems to be Solved by the Invention] The present invention has been made by focusing on the various problems mentioned above. It is thought that because the porosity and pore size of the compact are large and the strength is low, molten steel enters the pores during casting and solidifies, and the refractory is mechanically removed during intermittent drawing. The technical challenge is to improve corrosion resistance, thermal shock resistance, etc. that can withstand time casting. [Means for Solving the Problems] In order to solve the above-mentioned technical problems, the present invention has been made as a result of numerous studies on cast refractories. (1)
Although Si ₃ N ₄ exhibits corrosion resistance against carbon steel, it chemically reacts with stainless steel and causes _{erosion loss} . ₃ N ₄ forms a sialon-based solid solution and can significantly improve corrosion resistance. Pauling cracking is more likely to occur as the coefficient of thermal expansion and modulus of elasticity among the properties of refractories increases, and for this reason, it is possible to reduce the coefficient of thermal expansion and modulus of elasticity by uniformly dispersing BN in the solid solution. (The finer the BN particles, the better this effect) and (3) that reducing wettability and reducing pore size are effective in improving mechanical damage. By adding montmorillonite group minerals, especially bentonite, to the solid solution, it becomes difficult to wet with molten steel, and the reaction with sialon promotes bonding between particles to improve strength, and the glass layer that partially forms in the sintered body The present invention was achieved based on the discovery that during use, refractory blocks the pores and prevents the intrusion of molten steel, while also acting as a lubricant between the refractory and molten steel to improve corrosion resistance. That is, the present invention uses silicon nitride (Si ₃ N ₄ ) 10~
75%, aluminum nitride (AlN) 1-30%, boron nitride (BN) 3-30%, aluminum oxide 2
This is a method in which 50% to 50% of montmorilloid group minerals and 5 to 30% of montmorilloid group minerals are blended, kneaded, molded, and then sintered in a non-oxidizing atmosphere. By containing BN, thermal shock resistance can be significantly improved. The BN content is set in the range of 3 to 30%, but if it is less than 3%, there is no effect, and if it is more than 30%, the strength of the sintered body will decrease significantly. Si ₃ N ₄ can improve contact resistance to molten steel by containing AlN and Al ₂ O ₃ and sintering at high temperature to form a sialon-based solid solution. In this case, AlN is 1-30% and
Although it is necessary to contain Al ₂ O ₃ in an amount of 2 to 50%, below these lower limits, thermal shock resistance decreases. Furthermore, when bentonite is used as a montmorilloid group mineral, for example, Al ₂ O ₃ −, the main component of bentonite, is used.
Although some of the SiO ₂ components are solidly dissolved in SiAlON,
The alkaline component reacts with Sialon to produce a glass phase, which promotes bonding between particles, lowering the porosity and also lowering the wettability. Such montmorillonite group minerals are blended in a range of 5 to 30%. If it is less than 5%, wettability will decrease and there will be no effect of improving sinterability, and if it is more than 30%, a large amount of glass phase will be formed, resulting in poor high-temperature properties. decreases. In order to manufacture the continuous casting reinforced material of the present invention, first, each of the above-mentioned constituent components, namely, Si ₃ N ₄ ,
AlN, BN, aluminum oxide, and montmorillonite group minerals are blended in the above-mentioned amounts, kneaded, and molded using an appropriate molding means.
Preferably, sintering is carried out at a sintering temperature in the range of 1800°C for about 1 to 10 hours. [Effect of the invention] As mentioned above, the present invention has silicon nitride of 10 to 75%,
Aluminum nitride 1-30%, boron nitride 3-30%
%, aluminum oxide 2-50% and montmorillonite group mineral 5-30%, after kneading and molding,
By sintering in a non-oxidizing atmosphere, montmorillonite group minerals are further added to the sialon-based solid solution particles in which BN is uniformly dispersed, making it difficult to wet with molten steel. The reaction of the minerals promotes bonding between particles and improves strength, while the glass layer partially formed in the sintered body closes the pores and prevents molten steel from entering during use, while providing lubrication between the refractory and molten steel. A refractory that can act as a refractory and improve corrosion resistance can be obtained, and a connection refractory for horizontal casting that has excellent corrosion resistance, thermal shock resistance, and prevention of damage due to solidification shells can be formed. This also made it possible to cast high-alloy steel. [Example] Specimen of continuous casting refractory of the present invention (Test No. 1
-2) and conventional refractory specimens (comparative test Nos. 1 and 2) for comparative purposes were made from each component shown in Table 1.

[Table] Each specimen was made as follows: First, Table 1
Each component shown in the table is blended in the amount shown in the same table, each blend is mixed and kneaded using a stirrer and crusher type kneader, then PVA is added as an organic binder to these blends, and The mixture was homogeneously kneaded using a kneader. Each kneaded material was molded to 220 mm using a hydraulic molding machine.
The molded product was molded into a ring shape (outer diameter) x 190 mm (inner diameter) x 15 mm (thickness) and a bar shape (20 mm x 20 mm x 120 mm) at a molding pressure of 1 ton/cm ² . Next, each of these molded bodies was sintered at 1700° C. in a non-oxidizing atmosphere of nitrogen to produce specimens of the present invention and comparative specimens of various shapes. (1) Among the specimens, rod-shaped specimens were used to measure corrosion resistance to molten steel and contact angle with molten steel. In erosion tests to investigate corrosion resistance, carbon steel S50C and austenitic stainless steel were tested in a high frequency furnace.
Melt 10Kg of SUS321 (25Cr-20Ti) each,
The test piece was immersed in molten steel kept at 1550℃,
After holding for a period of time, the amount of erosion of the test piece was measured.
In addition, the contact angle was determined by placing stainless steel SUS on the plate of the test piece using a high-temperature microscope.
The temperature was raised to 1500°C, held, and the contact angle at that time was measured. The results of these erosion tests and contact angle measurements are shown in the lower part of Table 1. In the erosion test, in the case of stainless steel, the amount of erosion was 5.0 to 1.5 mm in the comparison specimen, whereas in the specimen of the present invention, the amount of erosion was extremely small, 0.1 mm or less, and in the case of carbon steel, the amount of erosion was less than 0.1 mm. It can be seen that the specimens shown in Fig. 1 do not suffer from melting damage at all. Regarding the contact angle, Si ₃ N ₄ −AlN−BN
When the system contains Al ₂ O ₃ , the contact angle increases,
Bentonite is further added to this (Test No. 1~
2) It can be seen that the contact angle becomes even larger than that of Comparative Test Nos. 1 and 2 without addition. Also,
The test specimens of the present invention in Test Nos. 1 and 2 were compared with Comparative Tests Nos. 1 and 2.
It can be seen that the porosity is lower than that of No. 2, and the strength is significantly improved. (2) For ring-shaped specimens, this ring refractory was set between the horizontal continuous casting mold and the tundish, and the mold diameter was 212 mm.
20 tons of stainless steel round billets were cast under the following conditions: mm, drawing speed 0.8 m/min, and drawing length 75 mm. The degree of erosion of the refractories by the solidified shell at that time was measured, and the results are shown in Table 2 below.

[Table] From Table 2 above, the depth of erosion of the inner surface of the refractory by the solidified shell is
In 2), the refractory was 5.0 to 2.5 mm, which was large enough to damage the mold edge, making stable casting impossible.
In case 2), the erosion depth was only 0.1 mm, which caused no problems during casting, and the mold was in good condition, indicating that stable operation was possible. In the above embodiments, a ring-shaped refractory was described, but the refractory may also be rectangular. It can also be used by connecting it to a mold.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of horizontal continuous casting equipment in which the refractory of the present invention is used. 1... Tandite, 2... Field nozzle, 3... Connecting refractory, 4... Mold, 5... Molten steel, 6... Solidifying shell.

Claims (1)

[Claims] 1. When manufacturing refractories that connect continuous casting molds and tundishes, 10 to 75% silicon nitride, 1 to 30% aluminum nitride, 3 to 30% boron nitride,
A method for producing a refractory for continuous casting, which comprises blending 2 to 50% of aluminum oxide and 5 to 30% of a montmorilloid group mineral, kneading and shaping, and then sintering in a non-oxidizing atmosphere.